Just because something is "natural" doesn't mean anything you do with it is moral. Sex is "natural", but fornication and adultery are condemned in the Bible. Drying, rolling and smoking pot isn't any more "natural" than fermenting grape juice or something else and getting drunk on it.

Ephesians 5:18 says,
"And do not get drunk with wine, for that is dissipation, but be filled with the Spirit". Drunkards are also listed in 1Corinthians 6:10 along with others who will not inherit the kingdom of God. Drug abusers are doing the same thing.